The international photographer (Jan-Dec 1934)

September, 1934 The INTERNATIONAL PHOTOGRAPHER Eleven the green portion of the filter, with the result that the picture on the screen is green. The unique feature which the Agfacolor film possesses precludes the necessity of extremely careful processing. Formulas are supplied by Agfa and these should be carefully compounded. It is advisable to use apparatus such as the Leitz developing drum, which is a cylindrical glass drum around which the him is wound and attached with clips. The drum is set upon two metal uprights and placed over a tray containing the solution. A small handle is provided for rotating the drum. Carl Zeiss also supplies developing apparatus for the color film in the form of a special developing frame. The formulas for processing Agfacolor film are as follows: Developer tor Agfacolor Film Metol -------- 200 grs. Sodium sulphite (anhydrous) 3*^2 ozs. Potassium bromide 85 grs. Water (85° to 95°) ---- 31^ ozs. The chemicals are dissolved in the order given. After cooling add: Ammonia (sp.gr. 0.91) 1 oz. Hydroquinone - 62 grs. Dissolve in 3l/2 ounces of water. For use mix one part of the above solution with 5 parts of water. Development in the above developer is 4 minutes. The film is then rinsed for one minute in running water and placed in the following reversing bath : Reversing Bath Potassium bichromate 1^4 ozs Sulphuric acid (concentrated) 2>y2 ozs. Water -------- 35^4 ozs. Add the sulphuric acid slowdy to the solution of the bichromate which should be quite cold. For use mix one part of stock solution with 10 parts of water. The film is placed in the reversing bath until all the silver has been bleached out, which will take about 2 minutes. It is then washed for 1 minute in running water. After being in the reversing bath for about 1 minute the film can be exposed to bright light. The film is now placed in the developer used before for its final development, which will take place in about 3 minutes. This operation is carried out in bright light. The film is washed for about 2 minutes and then hung up to dry, all excess moisture being removed with a moist chamois skin, viscose sponge, etc. All the above processing solutions are used at a temperature of 65° F. It is recommended that the film be treated with Agfacolor varnish after it has dried. It can then be cut up into the individual pictures, and the latter mounted between the regular 50 mm. cover glasses, the mattes being mounted on the outer surface of either of the glasses. D-76 Fine-Grain Developer: Despite the fact that paraphenylene-diamine formulas are greatly in vogue many photographers still prefer to use the D-76 formula for general work in which extreme enlargements are not required. Such photographers will be pleased to know that this formula is now packed in a ready-to-mix form containing the various chemicals in the required quantities, merely necessitating their solution in water. It is offered in different sizes of cans making 1 quart, ^ gallon, and 1 gallon of developer, respectively. Eastman has also recently announced a new alkalai called Kodalk, possessing the following characteristics and advantages: By Augustus WOLFMAN 1. It is more alkaline than borax and slightly less than carbonate. 2. It does not contain carbonate, does not evolve a gas in contact with acid, and therefore cannot produce blisters. 3. The degree of development and the time required to obtain a desired contrast may be modified by varying the amount of Kodalk in the developer. 4. The life of the average potassium-alum fixing bath is extended because Kodalk developers have much less tendency than carbonate developers to precipitate an aluminum sulphite sludge in the fixing bath. 5. Kodalk dissolves readily and does not tend to cake when added to the water. 6. It keeps satisfactorily in a well covered container. The modified D-76 formula in which Kodalk is substituted for borax is known as the DK-76 formula and is as follows : Developing Formula DK-76 Water (125° F. or 52° C.) 16 ozs. Elon -------- 29 grs. Sodium sulphite (dessicated) 3 ozs. 135 grs. Hydrochinone ----- 73 grs. Kodalk ------- 29 grs. Water to make ---- 32 ozs. Dissolve the chemicals in the order given. Over-exposure and Sharpness : Many photographers follow the old reliable rules, "Expose for the shadows and let the highlights take care of themselves," and "When in doubt over-expose." These golden rules have on many occasions aided the photographer in obtaining a suitable negative of the subject. The modern emulsion has considerable latitude and can stand quite a bit of over-exposure and still yield a negative replete with detail. However, we still insist that there is no substitute for a reliable exposure meter, and one should always be employed, for slight over-exposure may aid in obtaining detail in the shadows, but considerable overexposure has its evils. One of the things it is detrimental to is sharpness. The emulsion contains many layers of silver grains which can be reduced to metallic silver, the amount of reduction being dependent upon the exposure the film receives. Let us assume that to produce detail in a shadow it requires but one layer of silver grains. Instead the film is given an amount of over-exposure which will cause five layers to be deposited. The effect is the same as if one were to look through a fine mesh material. As successive layers of the material are added the greater is the diffusion of the light. Definition also suffers due to diffraction. It is always best to emplov an exposure meter, and if in doubt over-expose but slightly. 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